Organic light emitting diodes (OLEDs) are organic thin-film electroluminescent devices which have the advantages such as simple preparation process, low cost, low power consumption, high brightness, wide viewing angle, high contrast and ability of achieving flexible display, and have attracted great attention of people. As a new generation of display means, The OLED display technology has begun to gradually replace the traditional liquid crystal display technology, and is widely used in mobile phones, computers, full-color TVs, digital video cameras, personal digital assistants and other electronic devices. The OLED display technology is different from the traditional liquid crystal display technology, and an OLED device of an OLED display panel comprises an anode, a cathode and a light emitting layer that is interposed between the anode and cathode. Where a voltage is applied across the anode and the cathode, holes and electrons move to the light emitting layer, and holes and electrons recombine in the light emitting layer to emit light. However, the cathode in the OLED display panel is an active metal that is very sensitive to water vapor and oxygen in the air and is very easy to react with moisture and oxygen penetrated from the outside environment and affect charge injection. In addition, the water vapor and the oxygen that penetrate into the OLED device can also chemically react with the organic light emitting material in the light emitting layer to damage the organic light emitting material and greatly lower the light emitting efficiency of the organic light emitting material. As a result, the performance of the OLED display panel is degraded and its lifetime is shortened. Therefore, requirements on an OLED display panel in package are very high.